The living-rock cactus is one of the delightful surprises of the Big Bend country, when one realizes that what looked like a small low flat grooved rock, half covered with dirt, is actually a spineless cactus. The challenge is to find them when they are not in flower, since the late summer or fall blooms obviously make it "too easy". As with all cacti, you should admire but not remove them--many cactus species are, like this one, quite rare and getting rarer, and "cactus diggers" are a major culprit. (And it is, of course, illegal to remove them from any of the parks of the Big Bend region.)